<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 盒子的background-image属性可以用radial-gradient()形式创建径向渐变背景。 */
        /* background-image:radial-gradient(50% 50%,red,blue)   圆心半径，圆心颜色，外部颜色*/
        div{
            width: 200px;
            height: 200px;
            border: 1px solid #000;
            margin:10px;
        }
        div.b1{
            background-image: radial-gradient(50% 50%,red,blue);
        }
        div.b2{
            background-image: radial-gradient(30% 20%,red,yellow,green,black,blue);
        }
        div.b3{
            background-image: radial-gradient(50% 50%,white,rgb(186, 186, 199));
        }
        div.b4{
            background-image: radial-gradient(80% 80%,white,rgb(186, 186, 199));
        }
    </style>
</head>
<body>
    <div class="b1"></div>
    <div class="b2"></div>
    <div class="b3"></div>
    <div class="b4"></div>
</body>
</html>